Java DNS缓存查看器 [英] Java DNS cache viewer

问题描述

解决方案

这是一个脚本，以便您能够查看/转储由java.net api使用的DNS缓存？打印正和负DNS地址缓存。

  import java.lang.reflect.Field; 
 import java.net.InetAddress; 
 import java.net.UnknownHostException; 
 import java.util.ArrayList; 
 import java.util.Date; 
 import java.util.List; 
 import java.util.Map; 
 public class DNSCache {
 public static void main（String [] args）throws Exception {
 InetAddress.getByName（stackoverflow.com）; 
 InetAddress.getByName（www.google.com）; 
 InetAddress.getByName（www.yahoo.com）; 
 InetAddress.getByName（www.example.com）; 
尝试{
 InetAddress.getByName（nowhere.example.com）; 
} catch（UnknownHostException e）{
 
} 
 
 String addressCache =addressCache; 
 System.out.println（addressCache）; 
 printDNSCache（addressCache）; 
 String negativeCache =negativeCache; 
 System.out.println（negativeCache）; 
 printDNSCache（negativeCache）; 
} 
 private static void printDNSCache（String cacheName）throws异常{
类< InetAddress> klass = InetAddress.class; 
 Field acf = klass.getDeclaredField（cacheName）; 
 acf.setAccessible（true）; 
对象addressCache = acf.get（null）; 
 class cacheKlass = addressCache.getClass（）; 
 Field cf = cacheKlass.getDeclaredField（cache）; 
 cf.setAccessible（true）; 
映射< String，Object> cache =（Map< String，Object>）cf.get（addressCache）; 
 for（Map.Entry< String，Object> hi：cache.entrySet（））{
 Object cacheEntry = hi.getValue（）; 
类cacheEntryKlass = cacheEntry.getClass（）; 
字段expf = cacheEntryKlass.getDeclaredField（expiration）; 
 expf.setAccessible（true）; 
 long expires =（Long）expf.get（cacheEntry）; 
 
字段af = cacheEntryKlass.getDeclaredField（address）; 
 af.setAccessible（true）; 
 InetAddress [] addresses =（InetAddress []）af.get（cacheEntry）; 
列表< String> ads = new ArrayList< String>（addresses.length）; 
（InetAddress地址：地址）{
 ads.add（address.getHostAddress（））; 
} 
 
 System.out.println（hi.getKey（）++ new Date（expires）++ ads）; 
} 
} 
} 
  

Is there a way to view/dump DNS cached used by java.net api?

解决方案

Here is a script to print the positive and negative DNS address cache.

import java.lang.reflect.Field;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Map;
public class DNSCache {
  public static void main(String[] args) throws Exception {
    InetAddress.getByName("stackoverflow.com");
    InetAddress.getByName("www.google.com");
    InetAddress.getByName("www.yahoo.com");
    InetAddress.getByName("www.example.com");
    try {
        InetAddress.getByName("nowhere.example.com");
    } catch (UnknownHostException e) {

    }

    String addressCache = "addressCache";
    System.out.println(addressCache);
    printDNSCache(addressCache);
    String negativeCache = "negativeCache";
    System.out.println(negativeCache);
    printDNSCache(negativeCache);
  }
  private static void printDNSCache(String cacheName) throws Exception {
    Class<InetAddress> klass = InetAddress.class;
    Field acf = klass.getDeclaredField(cacheName);
    acf.setAccessible(true);
    Object addressCache = acf.get(null);
    Class cacheKlass = addressCache.getClass();
    Field cf = cacheKlass.getDeclaredField("cache");
    cf.setAccessible(true);
    Map<String, Object> cache = (Map<String, Object>) cf.get(addressCache);
    for (Map.Entry<String, Object> hi : cache.entrySet()) {
        Object cacheEntry = hi.getValue();
        Class cacheEntryKlass = cacheEntry.getClass();
        Field expf = cacheEntryKlass.getDeclaredField("expiration");
        expf.setAccessible(true);
        long expires = (Long) expf.get(cacheEntry);

        Field af = cacheEntryKlass.getDeclaredField("address");
        af.setAccessible(true);
        InetAddress[] addresses = (InetAddress[]) af.get(cacheEntry);
        List<String> ads = new ArrayList<String>(addresses.length);
        for (InetAddress address : addresses) {
            ads.add(address.getHostAddress());
        }

        System.out.println(hi.getKey() + " "+new Date(expires) +" " +ads);
    }
  }
}

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